Reinforcement bar and method of making same



J. D. STlTEs Aug. 6, 1946.

2,405,Z 74 REINFORCEMENT BAR AND METHOD OF MAKING SAME Filed July 24, 1943 2 Sheets-Sheet 1 lNEN TOR JOSEPH D 57/755 BY ATT NEY I Patented Aug. 6, 1946 REINFORCEMENT BAR AND METHOD OF MAKING SAlVIE Joseph D. Stites, Chicago, 111., assignor to American Isteg Steel Corporation, New York, N. Y., a corporation of New York Application July 24, 1943, Serial No. 496,024

8 Claims.

The invention relates to reinforcement bars v for concrete structures and the like, and to methods of manufacturing such bars to give them improved physical properties. It relates in particular, to improvements in the type of twisted reinforcement bar shown in my prior patents, No. 2,256,060, and No. 2,324,651, and in the manufacture of such improved bars.

It is known that the bond value of reinforcement bars for concrete structures can be increased by providing them with transverse, diagonal, or spiral ribs, and many forms of bar having such ribs have been devised. However, the forms of ribbed bar heretofore proposed have been unsuited inherently to twisted bar of the type shown in my prior patent, to which reference has been made above. In those patents, I have disclosed another form of transverse rib which is applicable to twisted bar of dumb-bell cross section for preventing rupture during the twisting operation. It has been an object of my present invention to provide an improved form and arrangement of transverse ribs in such twisted bar which will increase the bond value, and which will eliminate, or greatly reduce, the manufacturing problems encountered with spiral ribs and other rib forms of the prior art.

Twisted bars of the type disclosed in my prior patents, No. 2,256,060 and No. 2,324,651, possess recognized advantages over other types from the standpoint of tensile and bending strengths, as well as bond value. I have discovered that these advantageous properties can be enhanced still further by the provision of the novel rib form that I shall now described. I have discovered, also, that the twisting process can be utilized to give to the transverse ribs 3, configuration which is peculiarly adapted to increase bond values. Concomitantly with this discovery I have found that parallel transverse ribs which initially are spaced in a manner not calculated to have any important efiect on the tensile strength of the bar, can be so deformed during the twisting operation as to enable them to contribute substantially to the tensile strength of the bar, provided their original disposition and spacing bears a certain relationship to the pitch of the helix of the twisted bar. Accordingly, a. further object of my invention is to provide a method of increasing the tensile strength of a twisted reinforcement bar without increasing the weight of the metal in the bar per unit of length.

Another object is to provide an improved method of manufacturing reinforcement bars of the character described.

Another object is to provide a reinforcement bar which will increase the bending strength of concrete sections produced therewith to a greater extent than is possible with high bond value reinforcement bars of types known heretofore.

Other objects and advantages will appear as the description proceeds.

In the drawings, wherein I have illustrated certain preferred embodiments of my invention:

Fig. l is a plan view of a short length of reinforcement bar as produced by the first step of my process.

Fig. 2 is a view of the same bar after twisting and stretching.

Fig. 3 is a cross-sectional view of the untwisted bar, taken as shown at 33 in Fig. 1.

Figs. 4, 5 and 6 are cross-sectional views of the twisted bar, taken as shown, respectively, at 4-4, 55 and 6-6 in Fig. 2.

Fig. 7 is a view similar to Fig. 3, but illustrating a modified rib construction.

Fig. 8 is a view similar to Fig. 1, showing a further modification.

In accordance with the invention I first produce, as by usual rod rolling methods, a fiat bar of the general form shown in Figs. 1 and 3, having two parallel rod-like sections 9 joined by an integral Web ID. Each rod-like section 9 preferably is substantially circular in cross-section, or slightly ovoid as best shown in Fig, 3. The web l0 preferably has across-section made up of two opposed arcs which are tangent to the arcs of the sections 9.

A series of parallel transverse ribs I! extend across the web Ill and around at least one side of the section 9, and a second series of such ribs l2 extend across the web and around the other side of the sections 9. The two series of transverse ribs are arranged in staggered relationship, as clearly shown in Fig. 1, so that each rib I I is exactly half way between a pair of adjacent ribs lZ. For ease of rolling, the transverse ribs may be rounded, or may have inclined sides, as shown at l3, so that their cross-sectional configuration approximates a trapezoidal form.

The flat bar of Fig. 1 is twisted to produce the helical structure shown in Fig. 2. In this step of the method. the length of the bar pref erably is maintained constant. which means that the length of each rod-like section 9 will be somewhat increased. The stretching of the bar in this manner results in a desirable amount of cold working which improves the physical properties of the bar.

transverse rib. These conditions are illustrated in Figs. 4, and 6, where the intersections of the respective transverse planes-ei. e. planes normalto the axis of the heliceswith the transverse I ribs are shown at the portions which have been lined horizontally to represent the color blue. In other words, I have discovered that it is possible to so adjust the spacing and disposition of the ribs II and I2, formed by the rolling operation, in relation to the pitch of the helices produced by the twisting and stretching operation, that all planes normal to the axis of the helices will intersect at least a portion of a transverse rib. This means that the factor of longitudinal rib spacing helical pitch can be utilized in such a manner as to increase the tensile strength of the bar. I have found, for example, that when the ribs on each side of the bar are spaced apart by a distance equal to approximately of the major diameter, D, of the bar,1or less, a twisting to a helical pitch of 12/1 will result in the condition named, wherein all planes, normal to the axis of the helices will intersect at least a portion of a transverse rib. The width and shape of the transverse ribs will influence the spacing/pitch factor, so that in some cases a spacing larger than D will result in the desired condition described. Also, if the transverse ribs be given a slight initial pitch in they rolling operation, the spacing can be in.- creased, as I shall discuss later in describing a modified form of the invention. In every case the proper relation of spacing to pitch can be determined by simple experiment, following my teaching that the ribs must always be sufiiciently close together that, after twisting of the bar, no transverse plane can fail to intersect at least a portion of a rib.

When the transverse ribs are arranged in the manner I have described, twisting of the bar actually increases its minimum cross-sectional area. This may be seen from a comparison of Fig. 3 with any one of Figs. 4, 5, and 6. (Fig. 3 is a section of the untwisted bar.) In each case, the cross-sectional area is increased by approximately the amount shaded for blue. Fig. 4 is taken at the center of a rib ll opposite the web Hi. Fig. 5 is taken half way between a rib H and a rib 12. Fig. 6 is taken one-quarter of the way between a rib l l and a rib l2, i. e., half way between the, two extreme or limiting conditions represented by Figs. 4 and 5. Hence it will be seen that these views show representative sections and cover substantially all possible cases. In every case the cross-sectional area is substantially increased, with resultant increase in tensile, compressive, and bending strengths. This increase has been brought about by the combination of proper rib spacing and degree of twist without the necessity of rolling the ribs at an angle, or on a spiral which from a manufacturing standpoint is not practicable.

It will further be observed that the transverse ribs, while rolled initially at right angles to the longitudinal axis of the bar, in the twisted bar are arranged in general at an acute angle to the longitudinal axis of the bar. The ends of the ribs are reversely curved, as shown at a in Fig. 2, forming hook-like portions which are particularly effective in increasing bond between the reinforcement bar and the concrete of the structure in which it is used. I have found that concrete sections reinforced with bars of the form I have described, have increased bending strength. I attribute this improvement in part to the increased bending strength of the bar itself, and in part to the increased bond between the bar and the concrete.

The ends of the ribs l I and l2 preferably blend into the sides of the sections 9, as shown at M in Fig. 3, where they meet longitudinal ribs l5 extending along the edges of the bar. The ribs l5, besides increasing the bond value of the twisted bar, simplify the manufacture of the bar by reason of the provision for a certain amount of flashing between the rolls of the mill used in rolling the flat bar. These ribs, like the transverse ribs H and IE, may be rounded or may have inclined sides as shown so that they have a crosssectional configuration which is substantially trapezoidal in form. The ribs I5 may, if desired, be omitted.

If desired, the transverse ribs may join the longitudinal ribs in the manner shown in the modified embodiment of Fig. '7. Here, the transverse ribs l5, instead of blending into the wire sections 9, come approximately flush with the tops of the longitudinal ribs I5. Also the central portion of each rib I6 is made a little higher to further strengthen the web M, as shown at H. V

In Fig. 8, I have shown another modification of the invention in which the transverse ribs are given a slight initial pitch in the rolling operation. The series of ribs H! are arranged at an acute angle to the longitudinal axis of the bar. A second series of ribs 19 at the other side of the bar, likewise arranged at an acute angle to the longitudinal axis, are disposed midwaybetween the ribs IS. The two series of ribs are thus in staggered relationship. They are pitched in the same direction around the bar. In this embodiment, the spacing between the transverse ribs can be increased somewhat while maintaining the feature of increased minimum cross-sectional area in the twisted bar. The spacing and pitch of the ribs I 8, I9 as formed by the rolling operation is so adjusted in relation to the pitch of the helices produced by the twisting and stretching operation that portions of ribs on opposite sides of the bar will be brought into common planes normal to the axis of the helices, or so that all planes normal to the axis of the helices will intersect at least a portion of a transverse rib. In this case, the ribs I8 (and ill) may be spaced apart by a distance greater than /,;B when the helical pitch of the twisted bar is 12/1. The spacing may be as much as %D, or more, depending upon the initial pitch of the transverse ribs and to a certain extent upon the width or thickness of the ribs. In every case the proper relation of initial pitch to spacing to helical pitch can be determined by simple experiment, following, as before, my teaching that the ribs must always be sufiiciently close together that, after twisting of the bar, no transverse plane can fail to intersect at least a portion of a rib. I prefer a rib spacing of not over about %D to D for all forms of bar disclosed herein, but I do not wish to be limited to this exact proportion in view of the number of variables such as helical pitch,

rib thickness, etc.

The modified constructions of Figs. 7 and 8 are suggestive of certain changes which can be made in my preferred construction while retaining salient features of the invention. Other modifications will suggest themselves to those skilled in the art.

The terms and expressions which I have employed are used in a descriptive and not a limiting sense, and I have no intention of excluding such equivalents of the invention described, or of portions thereof, as fall within the purview of the claims.

I claim:

1. A method of manufacturing a reinforcement bar which comprises the steps of forming a bar having two parallel rod-like sections joined by an integral web and forming thereon a series of parallel transverse ribs extending across said web and around one side of said rod-like sections, and a second series of parallel transverse ribs extending across said web and around the other side of said rod-like sections, said two series of ribs being arranged in staggered relationship, and thereafter twisting and stretching the bar so formed to produce a helical tructure, the parallel ribs being spaced closely together so that, in the helical structure produced by the twisting and stretching operation, all planes normal to the axis of the helices will intersect at least a portion of a transverse rib.

2. A method of manufacturing a reinforcement bar which comprises the steps of forming a bar having two parallel rod-like section joined by an integral web and forming thereon a series of parallel transverse ribs arranged at an acute angle to the longitudinal axis of the bar and extending on both sides of said web and around one side of said rod-like sections, and a second series of parallel transverse ribs arranged at an acute angle to the longitudinal axis of the bar and extending on both sides of said web and around the other side of said rod-like sections, said two series of ribs being arranged in staggered relationship,

and pitched in the same direction, and thereafter twisting and stretching the bar so formed to produce a helical structure, the spacing and pitch of the rib being so adjusted in relation to the pitch of the helices produced by the twisting and stretching operation that portions of ribs on opposite sides of the bar will be brought into common planes normal to the axis of the helices.

3. A rolled and twisted reinforcement bar which comprises two rod-like sections joined by an integral web, the bar being twisted about its longitudinal axis into a helical structure comprising two helices having a common axis, and a series of integral parallel transverse ribs extending on both sides of said web and around at least .one side of said rod-like sections, said ribs in the vicinity of the web being arranged in general at an acute angle to the longitudinal axis of the bar and having reversely curved ends.

4. A rolled and twisted reinforcement bar which comprises two rod-like sections joined by an integral web, the bar being twisted about its longitudinal axis into a helical structure comprising two helices having a common axis, and a series of integral parallel transverse ribs extend- 70 ing on both sides of said web and around one side of said rod-like sections, and a seco d Series Of integral parallel transverse ribs extending on both sides of said web and around the other side of said rod-like sections, said two series of ribs being arranged in staggered relationship and being spaced closely together so that portions of ribs on opposite sides of the bar lie in common planes normal to the axis of the helices.

5 A rolled and twisted reinforcement bar which comprises two rod-like sections joined by an integral web, the bar being twisted about its longitudinal axis into a helical structure comprisme: two helices having a common axis, and a series of integral parallel transverse ribs extending on both sides of said web and around one side of said rod-like sections, and a second series of integral parallel transverse ribs extending on both sides of said web and around the other side of said rod-like sections, said two series of ribs being arranged in staggered relationship and being spaced closely together so that all planes normal to the axis of the helices intersect at least a portion of a transverse rib.

6. A rolled and twisted reinforcement bar which comprises two rod-like sections joined by an integral web, the bar being twisted about its longitudinal axis into a helical structure comprising two helices having a common axis, and a series of integral parallel transverse ribs extendmg across said web and around one side of said rod-like sections, and a second series of integral parallel transverse ribs extending across said web and around the other side of said rod-like sections, said two series of ribs being arranged in staggered relationship and the spacing of the ribs being so adjusted in relation to the pitch of the helices that portions of ribs on opposite sides of the bar lie in common planes normal to the axis of the helices.

7. A rolled and twisted reinforcement bar which comprises two rod-like section joined by an integral web, the bar being twisted about its longitudinal axis into a helical structure comprising two helices having a common axis, and a series of integral parallel transverse ribs extending across said web and around one side of said rod-like sections, and a second series of integral parallel transverse ribs extending across said web and around the other side of said rod-like sections, said two series of ribs being arranged in staggered relationship and the spacing of the ribs being so adjusted in relation to the pitch of the helices that all planes normal to the axis of the helices intersect at least a portion of a transverse rib while planes at selected acute angles to said axis of the helices and intermediate said ribs lie wholly between the ribs.

8. A method of increasing the tensile strength of a twisted reinforcement bar having two rodlike sections joined by an integral web, which comprises forming on the bar, prior to twisting, a series of parallel transverse ribs which are separated longitudinally of the bar but which are so spaced in relation to the pitch of the twist that,

after twisting, portions of said ribs will be brought into common planes normal to the axis of the twisted bar.

JOSEPH D. STITES, 

